Products are often manufactured based on physical and/or functional characteristics of one or more components included in the product. For example, a fuel injector must be manufactured with predetermined dimensions in order to be compatible with a host machine. Further, the fuel injector must be manufactured so that it performs in a manner required for proper operation of the machine. Also, a product may be composed of a number of components that each must meet physical and functional characteristics to ensure the product meets specified criteria. Accordingly, high quality, precise manufacturing is required to ensure a product will operate as expected and within acceptable tolerances.
To ensure a product is manufactured according to its specified criteria, manufacturers may perform quality control checks during and following a manufacturing process. For example, a manufacturer may determine the quality of one or more components that are included in a product prior to assembling them into the product. The quality determination for each component may be based on one or more parameters that affect the assembly or the function of the product. Although measuring the quality of components during an assembly operation may provide some insight on the quality of a product's components, the piece meal analysis of the individual components does not provide a reliable analysis of the product's overall quality.
To address these reliability problems, manufacturers may perform a First Test Pass (FTP) analysis that involves testing a manufactured product in a performance tester device to determine whether the physical and/or functional characteristics of a product's components are acceptable (e.g., within predetermined tolerances). Along with testing the quality of the manufacturing of a product, the FTP analysis may also provide a comprehensive test of manufacturing capability, quality control strategy, production environment, etc., since the criteria of a product (e.g., physical and functional) are being tested on the product's components as a whole. An FTP analysis produces a value called an FTP pass rate, which reflects the percentage of components tested that are acceptable. Most manufacturers aim for high FTP pass rates, such as 95%, because the pass rate directly affects profits. That is, if a product's FTP pass rate is too low, the product may have to be redesigned and/or remanufactured.
The FTP pass rate may be based on multiple factors associated with a manufacturing process such as: manufacturing capability, assembly procedure, measurement capability, sensitivity features, and FTP test criteria. Manufacturing capability reflects the ability of a manufacturer to meet predetermined design requirements, such as nominal measurements and tolerances. To minimize functional and/or physical variations in manufactured products, a manufacturer must also be able to minimize the ratio of a manufacturing range of specifications over a tolerance range of specifications, which is known as the Cpk factor. Assembly procedures also affect variation between products. For example, improper assembly procedures may increase assembly error, which in turn will lower the FTP pass rate for a corresponding product. Measurement capability reflects the ability to measure various types of characteristics of product components that are included in the assembly procedure. Errors in measurement may significantly affect the variation between product because the assembly process may be unnecessarily adjusted to compensate for incorrect measured component characteristics. Sensitivity features denote one or more features that have significant effect on the performance of a product. Finally, FTP test criteria are associated with standards for quality control based on customers requirements.
One conventional method for determining the quality of a assembly process is described in U.S. Pat. No. 5,452,218 issued on Sep. 19, 1995 to Tucker et al. The method described in the '218 patent includes collecting manufacturing capability data stored in a database to model a product to produce a measure of quality for the product. Although the method in the '218 patent provides quality information for a product, the method does not consider a combination of information such as manufacturing capability, assembly procedure, measurement capability, sensitivity features, and desired quality characteristics associated with the product. Accordingly, the measure of quality for the product are based on limited information leaving a product open to additional defect producing operations that are not accounted for by the method.
There is currently no method for analyzing and monitoring pass rates based on the relationship between the above mentioned factors. The present invention is directed to solving one or more of the problems set forth above.